The invention relates to a synchronization device for a transmission, having a sliding sleeve, a blocking synchronizer ring and a change wheel, wherein, in a force flow region between the blocking synchronizer ring and the change wheel, ramps for producing a servo force axial with respect to the shaft are provided on at least one component part.
In known synchronization devices, the sliding sleeve is connected radially on the outside for conjoint rotation to a synchronizer body mounted for conjoint rotation on a shaft, but is arranged in such a way as to allow axial movement toward the associated change wheel, wherein the change wheel is mounted as a free gear on the shaft. To connect the synchronizer body and the change wheel for conjoint rotation by means of teeth on the sliding sleeve which connect the two the rotational speeds of the synchronizer body and the change wheel must be matched or synchronized in a synchronization process. The blocking synchronizer ring is provided with blocking teeth and, for pre-synchronization, is coupled axially with a limited ability for circumferential movement to the synchronizer body. For synchronization, the sliding sleeve is moved against the blocking synchronizer ring in such a way that a force takes effect, introducing an axial shifting force in the direction of the change wheel to be coupled, the blocking synchronizer ring for its part exerting on the change wheel a circumferential force or torque by means of friction in order to brake or accelerate the change wheel to the rotational speed of the synchronizer body for the purpose of matching the rotational speeds. Until synchronism has been achieved, the blocking teeth of the blocking synchronizer ring are aligned relative to the teeth of the sliding sleeve in such a way that the latter strike against the blocking teeth and are thereby blocked axially. When synchronism occurs, the limited circumferential mobility of the blocking synchronizer ring enables it to be turned relative to the teeth of the sliding sleeve in oblique planes into a synchronized position, in which the teeth of the sliding sleeve and of the blocking synchronizer ring and the coupling teeth provided on the change wheel are in axial alignment and the sliding sleeve, reaching over the blocking synchronizer ring with engagement between the teeth, can engage in the coupling teeth and hence produce a connection for conjoint rotation between the synchronizer body and the change wheel.
To reduce the axial shifting force to be introduced via the sliding sleeve and/or to shorten the synchronization process, a self energizer which produces axial servo force is provided in more recent synchronization devices.
U.S. Pat. Nos. 5,135,087 C and 4,732,247 C each describe a synchronization unit of the type in question having the ramps for producing the axial servo force. Here, the blocking synchronizer ring and the synchronizer ring or intermediate cone and the change wheel engage in one another via radial projections with ramps.
As an alternative, it is possible, as described in DE 10 2005 056 827 A1, for the self energizer to be designed as a spring device having spring elements, wherein, when the sliding sleeve is moved against the blocking synchronizer ring, the spring elements press the latter toward the change wheel with a servo force.
In EP 1 219 847 B1 EP 2 169 250 Al and EP 1 900 956 A2, a servo force is produced by means of blocking pieces which are spaced apart circumferentially in a uniform manner and which, for pre-synchronization, simultaneously perform a conventional blocking function to block the sliding sleeve in the case of asynchronism. During synchronization, the blocking pieces are supported in the circumferential direction by means of a ramp as a force transfer surface on a corresponding ramp on the synchronizer body and, via the ramps, couple the axial servo force into the synchronizer ring in the servo force direction. This process is also described in VDI Report No. 1393 from 1998 (“Low Force Boost Concept for Baulk Ring Synchronizers”). The disadvantages with this, apart from a complex structure, are susceptibility with respect to axial tolerances and increased wear of the synchronizer rings. Owing to the angular positions of the blocking faces, these must be of correspondingly wide design and this, in turn, requires along sliding transfer phase and hence a long stroke of the sliding sleeve and ultimately an increased expenditure of force.